The present invention relates to ultraviolet (UV) light sources. In particular, it relates to microwave-driven ultraviolet light sources.
Excimers are diatomic molecules or complexes of molecules that have stable excited states with an unbound or weakly bound ground state. In principle, they can be formed by all rare gases and rare-gas halogen mixtures and in most cases, the reaction kinetics leading to the excimer is selective. Because these complexes are unstable, they disintegrate within a few nanoseconds converting their excitation energy to spontaneous optical emission. Re-absorption of this light cannot occur because these complexes have no stable ground state. In turn, it is possible to construct excimer lamps emitting light with a high intensity within narrow spectral regions in the deep ultraviolet (UV) region. Many materials absorb radiation at less than approximately 250 nm, making UV or visible-UV (VUV) sources important. In turn, these sources can selectively drive radical-mediated processes such as: UV curing, metal depositions, protective and functional coating, pollution control, photo-deposition of amorphous semiconductors, and photo-deposition of dielectric layers.
Many excitation techniques for excimer sources have been studied. Among them, microwave-drive is especially appealing because the underlying technology has been so extensively developed for other purposes and because no electrodes are needed, prospectively enabling long bulb life at high power.
Microwave-drives operating at frequencies above 1 GHZ require a carefully designed cavity for efficient coupling of the microwave energy into the discharge. This condition makes it difficult and expensive to increase the size and to construct an efficient UV source.
Therefore, it is an object of the present invention to provide a microwave-drive that does not require the use of wave guides, directional couplers, or tuners.
Another object of the present invention is to provide an over-moded microwave cavity wherein the probe of the magnetron is directly coupled to the cavity.
By the present invention, a microwave-driven ultraviolet (UV) light source is provided. The light source comprises an over-moded microwave cavity having at least one discharge bulb disposed within the microwave cavity. At least one magnetron probe is coupled directly to the microwave cavity.
In use, the microwave-driven UV light source is provided. A gas capable of forming an electronically excited molecular state is introduced into each discharge bulb. Pressure is applied at a range from about 10 Torr to about 50 Atm and power is input at up to about 50 kW.
Since the probe of the magnetron is directly coupled into the microwave cavity, it operates in an over-moded fashion, i.e., no one particular mode dominates. In turn, the over-moded operation eliminates the need for precise tuning during operation on a manufacturing floor, where the temperature and other environmental factors may vary. The design further eliminates the need for very precise control of the bulb shape and placement, offering easier maintenance and reliability. Lastly, the arrangement offers the highest likelihood of distributing power evenly between a multiplicity of bulbs sharing a common cavity.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.